In the case where it is desirable to control presses, machine tools, construction machines, ships, airplanes, unmanned or automatic carriers, unmanned warehouses or so on an integrated data processing basis, a multiplicity of sensors for detecting the states of the respective machines or warehouses and a multiplicity of actuators for controlling the states thereof become necessary. The number of such sensors and actuators amounts, in the case of the presses for example, to more than 3000 and in other cases, amounts to much more than the above.
Conventionally, there has been considered an integrated data processing system for controlling such sorts of machines or items on an integrated data processing basis, in which a plurality of nodes are connected in series, each of the nodes is connected to one or a plurality of sensors and actuators, and these nodes are connected in a ring form through a main controller so that each node is controlled by a signal received from the main controller.
In the case where the nodes are connected in series in this way, it becomes important how to secure the simultaneousness of outputs of the respective-sensors as well as the simultaneousness of control of the actuators. For example, when such an arrangement is considered that addresses are allocated to the respective notes and the nodes are controlled on the basis of the addresses, a time delay taken for the address processing becomes a problem, which results in that the satisfactory simultaneousness cannot be secured with respect to the collection of the outputs of the sensors and the control of the actuators.
To solve the problem, the inventors of the present application have suggested a series control system which nodes are connected in series, an idea of allocating addresses to the nodes is discarded and instead the nodes are identified by their connection sequence, whereby the need for address processing can be eliminated, the problem of the time delay caused by the address processing can be removed, and further the node structure can be remarkably simplified.
Such a series control system is arranged as shown in FIG. 4.
The series control system is suitably used in a centralized control system for controlling a press. In the system, a host controller 200 performs general control respective portions of the press. A main controller 100 controls data transfer with a plurality of nodes 10-1 to 10-N connected thereto. Groups of sensors 1-1, 1-2, . . . , and 1-N are provided to the respective portions of the press to detect the states of the press. Groups of actuators 2-1, 2-2, . . . , and 2-N are provided to the respective portions of the press to drive the associated presses. The sensor group 1-N and the actuator group 2-N are connected to the associated nodes 10-N (N=1 N) which in turn are connected in a loop form together with the main controller 100.
FIG. 5 shows frame structures of a data signal used in the system when the number N of nodes are set to be 5. The data frame signal is issued from the main controller 100, passed through the nodes 10-1, 10- 2, . . . , and 10-N and sent back to the main controller 100. FIG. 5(a) shows the data frame signal immediately after outputted from the main controller 100, FIGS. 5(b), (c), (d) and (e) show the data frame signals outputted from the nodes 10-1, 10-2, 10-3 and 10-4 respectively, and FIG. 5(f) shows the signal outputted from the node 10-5 (the signal to be fed back to the main controller 100 when N=5).
The contents of the respective signals having the frame structures of FIG. 5 are as follows.
STI; First start code indicative of the heading position of an input data (sensor data) DI PA1 DI; input data (sensor data) PA1 DIq; Input data from a sensor connected to the q-th node PA1 STO; Second start code indicative of the heading PA1 position of output data (actuator drive data) PA1 DO; Output data (actuator drive data) PA1 DOq; Output data to the actuator connected to the q-th node PA1 SP; Stop code indicative of the terminating end position of a data string PA1 CRC; CRC code for CRC check PA1 ERR; Code indicative of error presence or absence, error content and error position
The respective nodes 10-1 to 10-N shown in FIG. 4 operate to add the detection data DIq of the sensor 1 connected to the node to between the start codes STI and STO and to remove the output data DOq to the actuator 2 connected to the associated node from the output data immediately after the start code STO as shown in FIGS. 5 (b) to (f).
Accordingly, in this system, when such a data frame signal containing the actuator control data DO as shown in FIG. 5(a) is sent from the main controller 100 to the node 10-1, the data frame signal is sequentially propagated from the node 10-1 via the nodes 10-2, 10-3, 10-4 and to the node 10-5, which results in that the actuator control data DO in the data frame signal are allocated to the corresponding nodes and at the same time the detection data of the sensor group obtained at the respective nodes are taken into the data frame signal. As a result, when the data frame signal is fed back to the main controller 100, no actuator control data DO are contained in the frame signal and the detection data of the sensor group are contained in the frame signal as shown in FIG. 5(f).
The error code ERR in the data frame signal comprises, as shown in FIG. 6, a bit Ea indicative of the presence or absence of an error, an error content code Eb indicative of the contents of the error, and an error position area Ec indicative of the position of the error. When one of the nodes detects such an error as a communication error, this node sets the bit Ea at "1", sets the error content code Eb to have a code content corresponding to the generated error, and further initializes the error position area Ec to have such an initial value as "10 . . . 00) (which means a value "1", though the bit order is reversed). The data frame signal with such an error code ERR attached to the end thereof is sent to a next node in the next stage.
The node in the next stage, when receiving such an error code ERR, detects that the bit Ea in the error code ERR has a value "1", adds "1" to the data of the error position area Ec, and sends to a node in the next stage the data frame signal having the error code ERR attached to the end thereof. In this way, the subsequent nodes similarly operate to add "1" to the data of the received error position area Ec.
The data frame signal is thereafter applied to the main controller 100. The main controller 100 can know the generation of the error on the basis of the value "1" of the bit Ea, can know the error content on the basis of the error content code Eb, and also can know the position of the error generation on the basis of the value added by "1" to the data content of the error position area Ec. For example, in the system of FIG. 4, when N=5 and an error is detected at the node 10-3, the value added by "1" to the data content of the error position area Ec inputted to the main controller 100 corresponds to binary data indicative of a decimal number "4", so that the main controller 100 can detect the generation of the error at the node 10-3 through its reverse calculation.
When the main controller 100 detects the presence of an error in the data frame signal for the first time (when the bit Ea is "0" and the main controller 100 detects such an error as a CRC error), the error position area Ec has an eventual value of "1".
The initial set value and addition value of the error position area Ec at the nodes and the main controller are set by the following technique.
______________________________________ Sn 1 0 2 ADn +1 +1 +1 ADm +1 +2 +0 Sm 1 1 1 ______________________________________
Reference symbol Sn denotes the initial set value of the error position area Ec when the node detects an error, ADn denotes an addition value at the node, ADm denotes an addition value when the main controller detects that Ea=1, and Sm denotes the initial set value of the error position area Ec when the main controller detects an error for the first time.
With such a system, the main controller 100 is connected to an operating panel and a display unit for the input and output of various sorts of data, so that the contents of the generated error and the position of the error generation are displayed on the display unit. However, this prior art system is arranged so that the error content and error generation position discriminated at the main controller 100 are displayed directly on the display screen. That is, in this error display unit of the prior art, the display position corresponding to the error content and error generation position refers to one location, and the error contents and error generation positions at different time points reflect directly on the display contents.
For this reason, the prior art system has had a problem that, when errors frequently take place at a plurality of different locations, the error contents and error generation positions are frequently and complicatedly changed, with the result that the operator cannot confirm the error contents and error generation positions. Further the prior art system has had another problem that, since an error history is not recorded, the operator cannot judge the state of the currently generated error. In more detail, though the error generation states include generation of a multiplicity of errors at a multiplicity of locations, generation of a multiplicity of errors at a small number of regular locations, generation of a small number of errors at a multiplicity of locations, and error generation at a very low frequency, the prior art system cannot discriminate to which one of those states the current error belongs.
In view of such circumstances, it is an object of the present invention to provide an error display device of a data transmission system capable of easily confirming the display content regarding errors and the state of the current error.